Abstract
Polymeric gels are widely used in hydraulic fracturing operations to produce natural gas from tight sands. The recovery of injected gel is often poor and large quantities are left behind, which can cause a loss in gas productivity due to a reduction in the fracture conductivity. In this paper, we present a novel study of remediation of gel damage from proppant packs by dry gas injection. We experimentally investigated removal of polymeric fracturing fluid gels from proppant packs and recovery of gas flowrate at constant pressure drawdown conditions.
The gel removal process takes place in two steps, the first being a viscous displacement process which is followed by an evaporation process. Due to the high viscosity, gel removal by simple displacement is ineffective and only 20-30% of the gel is removed at high drawdown pressures and only 3-5 % of the undamaged flowrate is recovered. However, when dry gas is injected, the entire water content in the gel is removed due to evaporation. Results from experiments conducted with sandpacks and fracture-packs show that about 40% of the undamaged flowrate is recovered by dry gas injection. Additional treatment of the trapped gels with alcohol solvent shows that gas flowrate recovery is greater and achieved faster if the dry gas treatment is preceded by a single alcohol soak treatment. The alcohol treatment improves recovery of gas rate due to greater volatility which enhances the evaporation rates.
Dry gas injection is effective in removing water content of the gel from sandpack and fracture-pack. Hence the residual gel saturation is lowered, leading to greater gas relative permeability and gas flowrate. A mathematical model based on drying front propagation is developed to predict the rate of water removal and the recovery of gas rate in damaged laboratory scale fracture and sandpacks. The model prediction agrees well with experimentally observed gas flowrate recovery in gel damaged cores.
